Go to any large-scale outdoor event, like a music festival, and you'll be confronted by an array of public toilets—but some may not really be fit to use by the time you get to them. Here's how to ensure you get the best spot to relieve yourself, using math.

In this video, Dr Ria Symonds breaks down the problem, starting small and extending the theory to hundreds of toilets, so you can try and apply some logic next time you're caught short. Good luck! [Numberphile]